Collagen is the most common protein in the structural support of the human or mammalian body. Collagen's basic elemental unit is the tropocollagen protein. Tropocollagen is composed of three polypeptide chains of the same size. These chains are wound about each other forming a superhelical cable or a triple-stranded helical rod. Each of the three chains in tropocollagen consists of about a thousand amino acid residues.
Several different types of collagen proteins are currently recognized as distinct, differing in amino acid composition and length. Type I collagen is composed of two alpha-1(I) and one alpha-2 polypeptide chains. Type I collagen is mostly found in the supporting structure of skin tissue, tendon, bone and in the eye cornea. Type II collagen contains three polypeptide chains of the alpha-1(II) type and is found primarily in articular cartilage, within the intervertebral discs and in the vitreous body within the eye. Type III collagen is composed of three alpha-1(III) polypeptide chains and is found in tissues such as fetal skin, the cardiovascular system and reticular fibers in the eye. Type IV collagen has a mixture of two alpha-1(IV) and one alpha-2(IV) polypeptide chains and is primarily found in basement membranes. Type V collagen has two alpha-1(V) and one alpha-2(V) polypeptide chains and is found, e.g., in placenta and skin. Other types of collagen have comparable structural differences from one another.
Rheumatoid arthritis is a cell-mediated autoimmune disease, i.e., a condition where the immune system mistakenly perceives the body's own tissue as foreign and mounts an abnormal immune response against it. Rheumatoid arthritis is characterized by persistent inflammatory synovitis that causes destruction of cartilage and bone erosion, leading to structural deformities in the peripheral joints. Joints containing articular cartilage of which Type II collagen is a major component are particularly affected.
Rheumatoid arthritis is accompanied by joint swelling, inflammation, stiffness and pain especially upon flexing. In the advanced stages of arthritis, debilitating pain may result from even a slight movement of the joints. A substantial percentage of afflicted humans possess T-cells of the CD4+ type specifically reactive with collagen and/or have an abnormal humoral response against collagen.
Present treatment for arthritis involves use of nonspecific cytotoxic immunosuppressive drugs. These drugs suppress the entire immune system and are incapable of selectively suppressing the abnormal autoimmune response. This global restraint of the immune system over time increases the risk of infection. Non-limiting examples of such immunosuppressive drugs include methotrexate, cyclophosphamide, Imuran (azathioprine) and cyclosporin A.
Additionally, prolonged therapy with these nonspecific cytotoxic immunosuppressive drugs entails toxic side effects, including increased tendency towards development of certain malignancies, kidney failure, bone marrow suppression, diabetes and liver function disorders. Moreover, cytotoxic immunosuppressive drug therapy merely slows down the progress of the disease, which resumes at an accelerated pace after the therapy is discontinued. For example, about six weeks after such a drug is discontinued, the patient deteriorates to the same stage as before the treatment was begun. In addition, effectiveness of these drugs is self-limiting; they gradually cease being effective after about 2-5 years.
Steroid compounds such as prednisone and methylprednisolone (which are also non-specific immunosuppressive and antiinflammatory drugs) are also used for symptomatic relief. Steroids also have significant toxic side effects associated with their long term use.
Thus, current treatments for arthritis are of limited efficacy, involve significant toxic side effects, and cannot be used continuously for extended periods of time, which further limits their efficacy. Rheumatoid arthritis afflicts over 2 million individuals in the United States in any given year. Accordingly, there is an acute need for novel treatments and for novel therapeutic compositions for human rheumatoid arthritis that do not suffer from one or more of the drawbacks identified above.
An alternative treatment for arthritis is the oral antigen tolerization therapy proposed by the present inventors. It involves the oral administration of one or more tissue-specific antigens (i.e., antigens occurring only in the tissue under autoimmune attack) which have the ability to suppress the autoimmune response responsible for a particular autoimmune disease specifically, thus leaving other immune functions essentially intact.
The antigens useful in this approach generally include autoantigens, i.e., tissue-specific antigens that are themselves the subject of autoimmune attack. Pure bystander antigens, which are also tissue-specific (but are not the target of autoimmune attack) also possess the ability to elicit suppressor T-cells which are targeted to the afflicted tissue where they exert their immune suppressive activity via the release of immunoregulatory substances such as transforming growth factor-beta (TGF-.beta.), interleukin-4, or interleukin-10. These immunoregulatory substances in turn down-regulate all immune cells concentrated in the vicinity of the afflicted tissue, thereby suppressing immune responses in that locality. Bystander antigens include without limitation portions of autoantigens that (i) are not themselves the target of autoimmune attack and (ii) possess the requisite suppressive activity via elicitation of suppressor T-cells, i.e. are recognized by T-cells of the host.
Prior to the work of the present inventors, oral antigen tolerance therapy for arthritis had been tried only on artificially induced arthritis-like diseases in animals (adjuvant arthritis and collage-induced arthritis).
In the rodent models, collagen was shown only to prevent disease induction and had no or minimal effect on pre-induced disease. Oral antigen tolerization had never been tried in humans afflicted with arthritis.
Weiner et al., U.S. Pat. No. 5,399,347 discloses the oral administration of between 50 .mu.g and 10 mg and preferably between 100 .mu.g to 500 .mu.g per day of type II collagen, to treat arthritis in humans. At the time the invention of the '347 patent was made, 50 .mu.g per day was considered to be an extraordinarily small quantity of active ingredient for administration to humans for effective treatment of rheumatoid arthritis. It has now been discovered that even more effective and improved treatment of humans suffering from rheumatoid arthritis is obtained by oral administration of as little as 5 and typically 10-25 .mu.g per day, and preferably 20 .mu.g per day of type II collagen.
The discovery that 20 .mu.g of type II collagen per day is a more effective treatment for rheumatoid arthritis than higher doses is entirely surprising and unexpected. Classical pharmacology posits that a dose-response relationship exists whereby higher doses of a pharmacological agent give greater responses until a plateau is reached in the response. Lower doses should give lesser, not greater, responses. This would especially be expected to be the case with the present invention, which involves oral administration of a protein. Most pharmacological agents which are proteins must be administered via injection (e.g. insulin) because of the well-known destructive effects on proteins resulting from passage through the strongly acidic environment of the human digestive system. The finding that a lesser amount of orally administered type II collagen (on the order of 5 or 10 to 25 .mu.g) was useful in treating rheumatoid arthritis was therefore entirely surprising and unexpected.